Many Oakland properties are subject to local eviction controls. If your property is subject to these eviction controls and any of those units are tenant occupied, then you would need "just cause" to evict the tenants. An owner intending to make a unit his residence may be a just cause for eviction.
However, if more than one unit is tenant occupied, then there may be some issues/restrictions in evicting them for owner occupancy.
Anytime you need to evict someone from a unit that is subject to local eviction controls, then you should consult with an attorney familiar with those eviction controls. The Oakland eviction control laws are very complex.
If, however, the three units are vacant or the tenants have voluntarily vacated (no evictions needed), then you are entitled to occupy one or more of those vacant units. There is no maximum number of vacant units in your own property that you may occupy.